Internal combustion engines are used in a wide variety of applications to perform work such as moving a load. One common example is “over the road” or “on highway” vehicles, in which engines are used to drive or propel the vehicle. In these applications, engines carry out an internal combustion process in which the engine burns fuel to covert the potential or chemical energy therein to mechanical energy in the form of rotational torque. When employed on “over the road” vehicles, a drive train utilizes the rotational torque to propel the vehicle, for example, by using the torque to rotate a drive shaft that in turn drives the wheels or tracks of the vehicle. Torque, which is also related to power, is an important indicator of engine performance and further affects and influences many aspects of the internal combustion process.
U.S. Pat. No. 6,248,041 to Den Besten describes in part the relationship between torque and engine speed, and generally describes how a vehicle may be equipped with a computer or electronic controller for adjusting that relationship. The patent in particular describes systems and methods that adjust the torque and engine speed relationship as the vehicle shifts through various drive ratios for the purpose of imparting to the driver of the vehicle a feeling or sensation that the vehicle's power is in accordance with the drive ratio.
One well-known problem with internal combustion engines is that the combustion process can produce pollution byproducts and other emissions in the form of exhaust gases. To counter this problem, manufactures often employ a wide range of emissions control techniques and devices. Some common emissions control devices include mufflers, filters, catalytic convertors and the like that are added to the exhaust system and through which the exhaust gases must flow. Another technique to reduce engine emissions is exhaust gas recirculation (“EGR”) in which a portion of the exhaust gases are re-circulated back to the intake. The presence of the exhaust gases during the combustion process reduces the amount of nitrogen oxides produced by the combustion of fuel. As pollution and the environment becomes an increasing concern, government regulators are requesting that manufactures meet increasingly stringent emissions requirements, which manufactures may accomplish by the inclusion of additional emissions control devices or techniques on the engines or vehicles. A drawback of these types of emissions control devices and techniques are that they may negatively affect heat rejection from the engine. Internal combustion engines generate heat that must be removed to maintain proper operating temperature of the engine and prevent overheating and engine damage. Heat is typically carried away or removed via the engine exhaust, via water-side heat rejection (engine coolant), via air-side heat rejection (ATAAC), and via convection radiation. A large portion of the removed heat is carried away from the engine via the exhaust system. However, the added emission controls may insulate the engine and resist heat dissipation. Further, in order to ensure proper operating temperatures, the EGR process will necessitate increased heat rejection.
To supplement heat removal, many engine systems further include cooling systems that may circulate coolant through the engine. Such cooling systems are often designed or sized to provide sufficient cooling at a rated engine speed and at a rated load. Moreover, for aesthetic and aerodynamic reasons, manufactures often wish to minimize the size and prominence of the cooling system. However, as additional emissions controls are included, the increased heat load may overwhelm the cooling system. Accordingly, there is a need for an improved way to manage the heat produced by the engine while accommodating emissions control devices that may otherwise negatively affect heat rejection.